Mechanical Properties of Architected Nanomaterials Made from Organic–Inorganic Nanocrystals

Colloidal nanocrystals that consist of an inorganic core and an organic ligand shell can be assembled into architected nanocomposites. A wide range of mechanical properties can be achieved by tuning structural parameters such as sample dimensions, ligand length, and nanocrystal packing density. This review article describes the fabrication, structural characterization and nanomechanical testing of solid assemblies of nanocrystals. Self-assembly and solution processing techniques can be used to form freestanding membranes, thin films and 3D crystals that consist of ordered arrays, or disordered aggregates of nanocrystals. Membrane deflection, nano-indentation, and thin film buckling have been used to determine elastic properties, hardness and fracture toughness. Nanocrystal solids have elastic moduli of < 1–20 GPa, and hardness of ~ 40–450 MPa. Crosslinking of ligands and chemical sintering of inorganic nanoparticles can lead to dramatic improvements in stiffness, strength and toughness. The self-assembly of anisotropic nanocrystals can be used to make nanostructured materials with ordered porosity and 3D architectures.